(i) Field of the Invention
The present invention relates to a laser optical apparatus suitably used as an exposure device for exposing a photosensitive member in an electrophotographic system image forming apparatus.
(ii) Description of the Related Art
In the past, there have been a lot of image forming apparatuses such as laser beam printers, copying machines using laser beams, etc., which adopt an image forming process of a horizontal sheet feed type.
In recent years, however, there have come to be manufactured an increasing number fo image forming apparatuses of the type called a “vertical sheet feed type” in which a paper feed device is arranged at a lower portion of the apparatus, with sheets of paper fed by the paper feed device being conveyed in an upward direction from below to above so as to be discharged from an upper location.
This is due to the fact that in accordance with the progress of digitalization, it becomes possible to optically separate a document image reading device, which is in the form of a so-called image scanner for reading an original document, and an image forming part, which is in the form of an image forming process, from each other. Therefore, optical information read in by an image reading means can be replaced with an electric signal or an image signal by the use of a photoelectric conversion means such as a CCD or the like, and then the image signal thus produced can be sent through an electric line to an image forming part in the form of a printing part where it can be converted into an optical signal at an arbitrary location, which is in turn irradiated onto a photosensitive drum to form a latent image.
Thus, by using a laser beam as a writing means in accordance with an increased number of degrees of freedom of the writing position with respect to the photosensitive drum on which it becomes possible to set the position of irradiation of a laser beam at an appropriate location, an image forming process, which has been performed by using a horizontal sheet feed method in the past, can be carried out even by an image forming process using a vertical sheet feed method.
In addition, in an image forming means such as a developing device, a toner replenishment device, etc., in which toner is replenished from below to a photosensitive drum which is arranged at an upper location, technical advancements have been made in a drawn-up developing method of supplying toner to a developing sleeve disposed at a position higher than storage parts that store a developing material, toner and the like. Also, in connection with cleaning means, a lot of technical advancements have been made in downwardly directed cleaning means for performing cleaning in a reliable manner with an opening being directed downwardly in alignment and abutment with a photosensitive drum. As a result of such technical advancements, the image forming process according to the vertical sheet feed method has been made feasible.
Owing to the achievement of such an image forming process according to the vertical sheet feed method, it becomes possible for the layout of the image forming apparatus to take a short path configuration, as described below in detail. That is, a paper feed device including paper cassettes, a registration means, a photosensitive drum, a developing device and an image forming means including a cleaning means are sequentially arranged in a vertical direction from below to above, and at locations above these components, there can be arranged a paper conveying part and a fixing device, in the upper neighborhood of which there are also arranged a paper discharge means and a paper discharge opening. With such an arrangement, a short path configuration can be achieved without formation of any extreme bend of the conveying path extending from the paper feed means to the paper discharge means, thereby making it possible to shorten the travel or conveying distance of the paper and reduce the number of component parts required as well.
Moreover, the sheet conveying path can be vertically arranged in a relatively straight line, so that the space occupied by the sheet conveying path with respect to that of the entire apparatus can be reduced, thus making it possible to achieve reduction in size and cost as well as to shorten the time required for the paper to pass through the sheet conveying path. Furthermore, the increased number fo degrees of freedom of the layout serves to increase the density in arrangement of the component parts and save space as required, as a consequence of which the size of the entire apparatus such as an image forming apparatus can be decreased.
In addition, a lot of the following laser optical apparatuses have been used as a writing device for image exposure. That is, image information is emitted as a laser beam from a source of light using a laser diode, so that the laser beam thus emitted is irradiated onto a photosensitive drum while being scanned by means of a motor having a polygon mirror mounted thereon.
In such a laser optical apparatus, in order to ensure a specified degree of image quality by pinpointing a laser beam and providing a clear image, lenses are arranged such that the laser beam can be focused on the photosensitive drum.
Also, such a laser optical apparatus often uses about one to three reflection mirrors so as to provide freedom in the layout of the photosensitive drum and the laser light source thereby to change the direction of the optical path.
In order to satisfy demands or requirements such as the size, arrangement, etc., of a laser optical apparatus used in each product, it is necessary to individually design and fabricate such a laser optical apparatus for each image forming apparatus being used.